Composite materials comprising a mixture of a cellulose filler and a granular olefin series thermoplastic material are molded by compression molding, rotational molding, extrusion molding or injection molding, and such a composite material products are widely used in a variety of structural applications, such as in parts, panels, beams, boards and sheets. Mechanical properties, such as flexural properties, tensile properties and impact strength, of such composite materials are important considerations for their use in structural applications. There is a continuing need in the art to improve the mechanical properties of such composites. Additionally, there is a continuing need in the art to improve the service temperature, fire resistance and biological resistance of such composites.
U.S. Pat. No. 6,066,278 discloses a composite material composed of a wood cellulose filler and an olefin series plastic having a rigidity improving agent consisting of propylene modified by maleic anhydride and a carefully calculated amount of calcium oxide so that the water of the wood cellulose filler becomes finally 2–5% by weight. Since humidity varies from one location to another, the method disclosed in this patent is difficult as the correct humidity of the wood is not always easy to determine. This patent also teaches that the use of CaO requires surface treatment of the CaO.